Automated machine tool systems require a precise means of locating surfaces on workpieces. One of the most common methods is to have the machine move a probe into contact with the workpiece and to record the probe position when contact is made. Probes of this type are known as touch probes. They generally include a stylus for contacting the workpiece and circuitry which operates to generate an electrical signal when the stylus contacts the part. The machine controller can calculate information about the shape or location of the part from the X, Y and Z axes positional data of the probe when the stylus contact generates the electrical signal.
One of the problems encountered with the use of many of these types of probing systems is in the method by which the signal indicating contact by the probe is transmitted back to the controller. It is often impractical to rely on conventional wiring to carry the signal since the wires may interfere with normal machining operations.
The patent literature discloses several probe designs which are adapted to be used in an automatic machining center where the probes are temporarily stored in a tool magazine and are connected and removed from the spindle by an automatic tool changer mechanism. Representative examples of patents disclosing these probes include U.S. Pat. No. 4,339,714 to Ellis; U.S. Pat. No. 4,118,871 to Kirkham; and U.S. patent application Ser. No. 259,257 entitled "Apparatus For Detecting The Position Of A Probe Relative To A Workpiece", filed Apr. 30, 1981 by Juengel, now U.S. Pat. No. 4,401,945 which is assigned to the assignee of the present invention.
The Kirkham approach is disadvantageous because its radio frequency signals are susceptible to electromagnetic interference and must be used within a relatively short transmission distance between the probe and a receiver. Among the problems with the probe system of the Ellis patent is that great care must be taken to align the probe and a specially constructed detector on the spindle head in order for the reactive coupling therebetween to operate properly. The infrared transmission approach disclosed in the Juengel patent is far more advantageous. However, it does require that the probe, in most circumstances, contain its own power source.
It has also been proposed to use touch probes in turning centers such as lathes, as well as in machining centers. Turning centers differ from machining or milling centers in that the workpiece is rotated instead of the tool. In most turning centers, the tool holders are mounted at spaced locations about a turret which operates to selectively advance one of the tools towards the workpiece to perform work thereon. In general, tools for performing outer dimension work on the workpiece are mounted in slots within the turret whereas inner diameter tools such as boring bars are held in an adapter mounted to the turret.
Touch probes used in turning centers have a somewhat different set of problems to overcome than probe used in machining centers, although the method of transmitting the probe signal back to the controller remains a common concern. One of the problems unique to turning center application is that the probes remain fixed to the turret even when not in use unlike the situation with the machining centers where the probes are inserted in the spindle only when they are needed to be used. Consequently, it is not possible to rely on the probe insertion operation to activate the electronic circuitry therein.
One prior touch probe technique for turning centers utilizes inductive transmission modules to transmit the probe signal through the turret to the controller. See, e.g., LP2 Probe System literature of Renishaw Electrical Limited. Unfortunately, this technique requires a substantial modification of the turret in order to utilize the system. Consequently, this approach does not lend itself to be easily used in existing machines without requiring the expense and machine down time to perform the retrofitting operation.
Also related to this invention, although less directly, is that prior art concerned with wireless transmission of dimensional gauging data such as disclosed in U.S. Pat. No. 3,670,243 to Fougere; U.S. Pat. No. 4,130,941 to Amsbury and U.S. Pat. No. 4,328,623, to Juengel et al.